Lightning-arrester connection



' 1,636,544 July 1927' A. ATHERTON LIGHTNING ARRESTER CONNECTION Filed April 21. 192:5 2 Sheets-Sheet 2 WITNESSES INVENTOR Patented July 19, 1927.

f UNITED PATENT ALFRED L. ATHERTON,-.OF PITTSBURGH, PENNSYLVANIA, ASIGNOBrTO WESTING:

HOUSE ELECTRIC & MANUFACTURING- COMPANY, A COREORATION OF PENNSYL- VIANIA.

LmnTmne AnnEsrnn connno'rlon.

Application filed April 21, 192;. Serial 11 ,633,743.

This invention relates to excess voltage protective devices; more particularly to lightning arresters and to means for so eonneoting such devices as to give a maximum of protectionto the system in which they are incorporated.

It has been common rnctiee in eonnectine i t 7 3 valve-type lightning arrester elements in three-phase alternating current circuits; to use the so-cfalletl' multiplex connection wherein one element is interposed between each line or phase "Wire and the ground, the lower ends of said elements being connected together and another lightning arrester element inte'rpos d between this conneetion or netiti'al anil the ground. Such arr-esters are (leseriheil, tor example, in the patents to E. FL Creighton, Nos. 923,024; 923,338 and 933,826.

In ekeess voltage surges from exterior sources, such as atmospheric disturbaniresor lightning disoharges, the three-phase wires areall 'chargedto approximately the same excess voltage relative to the ground. In discharging the excess potential through the lightningarr-esters, the surge currents of the three lines 1 ass through the three line elem'ents and then combine at the neutralnnd pass tlii-ouglrtl eground element to ground. The impedance to the flow oi tl'i'esurgeeurrent' vell reeognized to of great inr portancein the performanee oi the lightning arrester and this impedance should be considererl at the voltage vhichthe lightning v permits to exist on the line. In otherwords', the major portion oi the surge currentinust flow'tl' rough the arrester'at such a safe voltage as to prevent accidental injury to the apparatus in. the circuit In tliewell known multiplex CODllGC-nlO'fl, with a lightning discharge passing through the e'ircu'it', the surge current flows through each of 'the' line" elements and then through the grouncl element, giving atotal efieotive impedance (11 03 5 for eaehoii' the surge ourrents equal to four timesthat of a single lightning'iarrester element-because ofithe faet that only On tlllld or the erc ss 'sectional area of the ground element is available fordiseharge'ot the surge current freineaoh line.

The disadvantages of the multiplex connection are] obviated by my invention, it be ing ainong'the ejects thereof to provide arrangement ,of protective elements ivhieh tio'ns.

"Inthe accompanying drawings constituting a part hereof and in \vh'eh like refereii'ce characters inclieate like pal s, V l

' Fig. 1 is a cliagr animatie view showing the 01d and WelLknown' multiplex connection protectiveelements for a 'three ph ase tem";

Fig. 2 t diagrammatic view showing one embodiment of'inyinventioni Fig. 3 is a diagrammatic view showingthe erred form of my invention, and Fig. Ms an elevational view' of a lightning arrester embodying the principles (it my invention. i i

shown in Fig. 1, each oi the phases of the alternating :current'systeni in the sun tiplex connection has protective elements '1 2 and 3 of a discharge voltage"designated as E, corresponding to-the volta from line to neutral so to break tlown'at a prede teri'ni'ned voltage sufiicient to prevent the flow of" dynamic currentuinler line voltage conditions out which allows anovervoltage to be discharged, such protective elements being eoiniiionly us? 'gna ted as lightning arresters'of the valve type. The elements are connectedtogether at i and a similar ground element 5 is conneeted thereto and togrouncl 6. In easea lightningdisoharge strikesthe system, the excessvoltage causes a break down of elements 1,2 an'cl 3,-the surgep assing therethrough to' connection a and t rough elements) to ground] Because of the necessity of the surge current from all the phases passing through element 5, the total effective impedanze drop oausecl by the floiv o f the surge currentin any phase is four times that of a single'element. This greatly debreases the protective value of the up paratus; i i I To obviate the disadvantage of the above connectionfl have flevise'd a nevi system siieh as shown inTF 2 embodyingthe phase l ii elements 1, 2 and 3 having the connection 4 therebetween as in the multiplex system. But in place of the single element 5, I insert elements 7, 8 and 9 in series with elements 1, 2 and 3, respectively. The latter elements are interconnected at 10 and are connected to ground 11.

When a lightning discharge strikes the system, the surge currents pass through the phase elements 1, 2 and 3, being equalized by the connection 4 and they then pass through elements 7 8 and 9 to ground. It will be noted that the impedance drop in the protective devices caused by the flow of surge current is twice the impedance drop in single element. This is in contrast to four times the impedance drop in the multiplex connection. Thus, by the addition of 50% to the number of elements, the protective values of the apparatus has been doubled. It follows that, in order to obtain equal protection, the elements of my system ma be half the size of those used with the mu tiplex connection.

I have discovered that still better results may be obtained by providing certain proportions of protective elements to give a still greater freedom of discharge for surge currents, as illustrated in Fig. 3. I provide protective elements 12, 13 and 14 connected to the phases of the circuit to be protected, each of the said elements having a discharge voltage corresponding to the voltage E from line to neutral, i. e. to approximately .58 of the voltage from line to line.- The said elements are interconnected at 15 and similar elements 16, 17 and 18 are connected in series with elements 12, 13 and 14, respectively, the elements 16, 17 and 18 each having a discharge voltage corresponding to .42 of the voltage from line to line or to .72 of the voltage E from line to neutral.

The ground elements are interconnected at 19 and are grounded at 20. Each line is thus connected to ground through a valve arrester unit or leg having a discharge voltage corresponding to the voltage from line to line, the individual units or legs having a neutral interconnection at a point corresponding to the voltage from line to neutral,

In the operation of this preferred form of my invention, when a lightning discharge strikes the system, the same passes freely from each of the phases or lines through its phase and ground elements to ground. The protective value of the lightning-arrester connection of Fig. 3 against the passage of the surge current is 2.32 times that of the multiplex connection of Fig. 1. Should difi'erences in voltage occur between the phases of the circuit, as, for instance, between phase 1 and phase 2, a discharge will pass from element 12 through connection 15 to element 13, thus equalizing the voltage between the phases. It will be noted that this form of my invention allows substantially a maximum freedom of discharge from one phase to another as well as from a phase to ground by interposing between points having certain differences of potential protective elements proportional to such differences of potential. I

In the practical embodiment of my invention, I provide a series of lightning arresters 21, 22 and 23, each of which consists of a plurality of protective units 22 with interposed rain shields 23 mounted upon a suitable support 24. In series with the protective units 22 is a gap 25 having a protective shield 26 thereover, the elements of the gap being supported on an insulator 27 and a conducting pillar 28, respectively. This construction is described and claimed in my copending applications, Serial No. 630,270, filed April 6, 1923, and Serial No. 633,742, filed April 21, 1923, for lightning arresters. The protective elements 21, 22 and 23 are interconnected by connections 15 at a point approximately 58% of the impedance of the elements from the line to ground. The supports 24 are electrically connect-ed by connections 19 and grounded. It will be noted that in a practical construction, such as is shown in Fig. 4, I utilize only three protective elements, each of which is of a capacity only slightly greater than those used in the multiplex connection but the impedance drop of the system to surge currents as compared to that in the multiplex connection is in the ratio of one to 2.32 with an increase of only 30% in the number of elements 22 employed. For practical reasons the arrester elements are built up from individual units of a standard size, as shown at 22 in Fig. 4, each unit having substantially the same breakdown voltage and the same impedance.

The cost of making the connections for my new system is practically negligible, it being only necessary to secure connectors 15 at t and, by a simple change of this character, the result is a great increase in facility of discharge with only a slight increase in the number of elements hitherto utilized.

I claim as my invention:

1. An excess-voltage protective system for multiple-phase circuits comprising a plurality of excess-voltage protective devices connected to the several line conductors of said circuits, :1 star-connecting means for said devices having a negligibl small impedance to excess-voltage disc arges, and excess-voltage protective means connected between the star point and ground, the discharge current-carrying capacity of said means being equal to the combined currentcarrying capacities of all of said star-connected protective devices,

2. An excess-voltage protective system for e proper point of the rain shields 23, Y

polyphase circuits comprising a plurality of excess-voltage protective devices connected in star to the several line conductors of said circuits, and excess-voltageprotective means connected between the star point and ground, the discharge voltages of said lineconnected devices being substantially pr0- portional to the star-voltage of the line, ZLIlC the discharge voltage of said grounded means being substantially proportional to the difference between the mesh and star voltages of said line.

An excess-voltage protective system for a three-wire three-phase line comprising a plurality of excess-voltage protective devices con acted in star to said line, and excessvoltage protective means connected between the star point and ground, the discharge voltages of said line-connected'devices being substantially proportional to the star-voltage ot the line, and the discharge voltage or said g ounded means being substantially proportional to 072 of said star voltage.

l. An excess-voltage protective system for a three-wire three-phase line comprising a plurality of excess-voltage protective devices connected in star to said line, and excessvoltage protective means connected between the star point and ground, the discharge voltages of said line-connected devices being substantially proportional to the starvoltages of the line, and the discharge volt age of said grounded means being substant ly proportional to 0.72 of. said star voltand the current-carrying capacity of a. t grounder l means being substantially equal to the combined current-carrying capacity of all of said line-connected devices.

5. An excess voltage protective system for three-phase circuits comprising a protective element for each phase, said elements being connected to ground, and an interconnection between said elements at a point approxi mately 58% of the impedance of each element from the line.

6. An excess-voltage protective system for three-phase circuits comprising a protective element t r each phase, said elements being connected to ground, each of said elements comprising a plurality of similar valve-cell units connected in series to have a total breakdown voltage correspondlng to the voltage from line to line.

7. An excess voltage protective system for three-phase circuits comprising a protective element for each phase, said elementsbeing connected to ground, each of said elements comprising a plurality of similar valvecell units connected in series to have a total breakdown voltage corresponding to the voltage from line to line, and an interconnection between said elements at a point approximately 58% of the impedance of each element from the line.

8. A protective device for a polyphase line comprising a valve-arrester )hase element for each phase of said ine, each phase element having a breakdown voltage and a discharge impedance proportional to the voltage from each line to neutral, said phase elements being connected in star, and an additional valve arrester ground element connected between the star point and ground, said additional ground element having a current discharge capacity equal to the com bined current discharge capacity of the several phase elements connected in parallel, the breakdown voltage of said ground element being so proportioned that the total breakdown voltage of a phase element and the serially connected ground element is substantially proportional to a voltage not less than the voltage from line to line and less than double the voltage from line t neutral.

9, An excess-voltage protective system for polyphase circuits comprising a protective element for each phase, said elements being connected to ground, each of said elements comprising a plurality oi similar valve-cell units connected in series to have a total breakdown voltage corresponding to the voltage from line to line, and an interconnection between said elements at a point corresponding to the voltage from line to neutral.

In testimony whereof, I have hereunto subscribed my name this 14th day of- April, 1923.

ALFRED L. ATHERTON. 

